The invention is directed generally to a mounting structure for semiconductors, and more particularly, to a mounting structure for mounting a heat generating triac type semiconductor onto a heat dissipating device.
In recent years, semiconductors, and in particular triacs, have been used with increasing frequency in various industries. Such semiconductor devices generate considerable heat which must be dissipated in order to preserve their operation and not damage the semiconductor material. Therefore, it has been customary to mount such semiconductors on what commonly is referred to as a "heat sink". The heat sink generally is a metal structure, frequently electrically conductive, having the property of relatively rapid heat dissipation. The triac switching device generally utilized consists of a body portion containing the semiconductor, a plurality of electrical leads protruding from the body portion in one direction, and an apertured metallic mounting tab carried by the body portion and protruding therefrom in a direction opposite to the electrical leads.
One conventional technique for mounting such semiconductor switching devices has been to thread a screw or other fastening device through the apertured mounting tab and into the associated heat sink. Also, in mounting switching devices of this character, a soldering operation frequently is required to secure the leads to the associated electrical connector. One problem encountered when using mounting screws in this manner is that as the screw is tightened, the body portion containing the semiconductor device may tend to turn, causing the protruding electrical leads to become twisted and possible short circuits to be produced. Another problem associated with the use of a mounting screw passing through the metal mounting tab, is the requirement that the screw be electrically isolated from the body portion of the switching device or from the electrically conductive heat sink by means of insulating bushings or other means. Also, the entire unit may have to be electrically isolated from an electrically conductive heat sink by the use of insulating paste under the triac which paste tends to be messy and time consuming to apply.
In order to maximize heat dissipation, it is desirable to maintain the metallic mounting tab of the switching device in substantially intimate contact with the heat sink. To accomplish this, it has been the practice in some instances to provide a metal spring associated with the housing structure for the purpose of biasing the mounting tab into good heat conductive relationship with the associated heat sink. However, the use of such springs raises other attendant disadvantages such as the possibility of the springs breaking or falling out of the housing or effecting a short circuit therein or requiring additional insulation steps as well as assembly steps to assure that the switching device will be electrically isolated from the associated heat sink.
Other problems which occur in mounting the switching device of the character described are encountered when the device is to be located in a high temperature environment. In such instances it may also be desirable to shield the semiconductor body portion from the ambient environment while still providing a means for mounting the device to a heat sink to dissipate the heat generated during the switching operation.